Magnetostrictive vibrator



June 12, 1934. w, P|ERE 1362,154-

MAGNE'IOSTRICTIVE VIBRA'I'OR Filed April 25, 1928 Patented June 12, I934 MAGNETOSTRICTIVE VIBRATOR George W. Pierce, Cambridge, Mass.

Application April 23, 1928, Serial No. 272,032 In Canada December 31, 1927 3 Claims. (Cl. 250-36) The present invention relates to electrical syselectric current or voltage in the coil. The in tems and apparatus, and more particularly to crement of magnetization depends upon the systems and apparatus for producing and susnature of the preexisting magnetic field and the taining electric, magnetic and mechanical oscilmechanical deformation. This reaction will, for

5 lations. From a more limited aspect, the invenbrevity, be hereinafter referred to in the speci- 60 tion relates to the frequency control and the frefication and the claims as the response. quency stabilization of the electric oscillations ,If the current or voltage is alternating, the of electric circuits, and to the transfer of periodic, electromagnetic field created thereby will also be electric energy from one electric system to alternating. The core 2 will, therefore, increase another. and decrease in length (let us say) many times a 65 The chief object of the present invention is to second, every variation in the current producing provide novel oscillators and oscillating systems its stimulative effect on the 'core 2 and every embodying magnetostrictive vibrators. deformation of the core producing its reaction Other objects will be explained hereinafter response upon the current; The core 2 will, in

and will be particularly pointed out in the apconsequence, freely vibrate mechanically by mag- 70 pended claims, it being understood that it is netostriction about a nodal point at its center intended to set forth, by suitable expression in with a period of vibration equal to the period of the claims, all the novelty that the invention may the alternating electromotive force. Ordinarily, possess. these vibrations will be quite small. When the In the accompanying drawing, Fig. 1 is 2. diaalternating frequency is close to, or substantially 7 grammatic view of a novel oscillating system acthe same as, the natural frequency of mechanicording to the present invention; and Fig. 2 is a cal vibration of the core 2, however, the amplisimilar view of a modification, tude of vibration of the core, though still small,

A magnetostrictive core 2 is shown axially posibecomes relatively quite large. The core will tioned within an inductive and resistive field coil, then react inductively on the load to render its 89 indicated in the figures by the numerals 10, 22 consumpton of power critical as to frequency for and 24. The core 2 may be in the form of a tube, frequencies near the free frequency of the core. or a rod, or it may be otherwise constructed. It The mechanical damping of the core, mounted is preferably of nickel, nickel-steel, nickel-copas shown, is as small as possible, with the result 20 per, nickel-cobalt, chrome-nickel, chrome-steel, that the resonant response of the core is very S or of any other metal element or alloy charac sharp and pronounced. Of course, there will terized by comparatively large magnetostrictive usually be more than one specific frequency of effects. By proper choice of length and other dimagnetization at which the core will thus mensions, the apparatus is applicable to systems resonate; for, in addition to one or more natural of high or low frequency within a range that may fundamental frequencies of mechanical vbra- 90 extend from a hundred cycles to hundreds of tion, it has also frequencies of vibration deterthousands of cycles. mined by the operation of the core in halves,

The core 2 may freely rest centrally upon a thirds, fourths, fifths, etc. The theory of this support 6, or it may be centrally clamped between operation is explained more at length in Letters the support 6 and a second clamping member 8, Patent No. 1,750,124, granted March 11. 1930, and as illustrated in Fig. 1, or it may be otherwise it will be sufficient here to remember that the supported. When an electric current is passed operation described herein is equally applicable through the coil, a magnetic field will be estabto the fundamentals and to their overtones. lished that will cause very slight mechanical dis- According to a feature of the present inventortion or deformation of the core 2 by magnetotion, the movements of the magnetostrictive de- 109 striction. The resulting increment of deformavice may be employed to effect the modulation of tion'may bealengthening orashortening, or some a local current. The modulations of the local other distortion, depending on the material and current may be utilized to send current back on the polarity of the increment of the magnetic through the coil so as to produce sustained cscilfield. This action of the magnetic field upon the lations, with a constant frequency determined by core 2 will, for brevity, be hereinafter termed the natural period of one of the modes of mestimulation. Conversely, any mechanical defchanical vibration of the core. One such novel ormation or distortion of the core will cause a oscillating system is illustrated in Fig. l. The magnetostrictive reaction upon the electromagcore 2 is held axially of a magnetic field pro- 55, netic field, and this will have its effect upon the duced by coils 22 and 24 by means of thecentrally 0 positioned clamps 6 and 8, so as freely to vibrate longitudinally about a nodal point-at its center, For symmetry, one of the coils is positioned on one side of the middle of the core 2 and the other on the other side. The coils may be compacted near the center of the rod, or they may be separated or spread out, each over the whole region of the half-length of the rod, or they may be replaced by a single coil. The field coils 22 and 24 of the core 2, being communicated to the supports 6 and 8, will cause variations in the electrical conductivity of the microphone '71. The circuit of the winding 69 comprises, in addition to the microphone 71 and the support 6, the support 8 and a battery '73. A tuning condenser, not shown, may be shunted about one or both of the coils 22, 24.

The theory of the oscillator of Fig. 1 is probably somewhat as follows: Fortuitous variations of plate current effect magnetization of the magnetostrictive coreyand the latter becomes magnetostrictively deformed, and the core is started in vibration. These vibrations are transmitted to the supports 6 and 8, causing changes in the electrical conductivity of the microphone 71. Variable electromotive forces are thus generated in the winding 67 through the winding 69-. With proper polarity of the transformer, this varies the current in the coils 22 and 24, varying the stimulation of the core. The core then causes further electrical changes in the winding 69, and so on. The local current of the battery 73, sent through the microphone 71, becomes thus modulated in accordance with the current of the battery 18 and acts inductively on the grid-filament circuit 26, 32, 6'? of the tube 30. The system will oscillate at 'a frequency determined by the fre-- quency of mechan cal vibration of the rod.

It is not essential that a vacuum tube be employed in order to produce oscillations. In the system of Fig. 2, the winding '75, in the local circuit with the microphones 15, 17, and the battery 11, is coupled to a winding '77 in a secondary c-rcuit with the coil 10 and the tuning'condenser 13. The energy of the battery 11 in the local circuit is thus transmitted inductively through the windings 75 and '77 to the driving coil.10, and the energy is fed back, magnetostrictively to the coil '75, and so on. The system thus drives itself, and here, again, the frequency of the oscillations is substantially constant and equal to the natural frequency of mechanical vibration of the core.

One of the important characteristics of this invention is that the core 2 may itself be a tuned element of very low decrement, so as to dispense with or supplement electrical tuning of the circuits. Greater sensitiveness and selectivity may,

however, be obtained by electrically tuning the signal circuits in any well known way. The local adjustable condenser 18 in the secondary circuit enhances the operation.

Of course, the microphones 15, 1'7, one or both, and the microphone 71, may be replaced by any other variable-resistance or variable-contact devices, or by any equivalent device for varying the electrical conductivity in response to mechanical deformations of the core, and preferably attached to, or forming part of, the core 2. In particular, the core itself may be an element of variable resistance.

The magnetostrictive core may either be permanently magnetized, or it may be magnetized electromagnetically from a local source, as by the batteries 18 and 81. The battery 81 further supplies the field winding 10 of the oscillator with direct current through a choke coil 83.

The oscillator may, of course, be used to supply a load 85, either directly, or through tuned circuits. This may be effected by taking off the power developed in the oscillator inductively by a coil 87, through a transformer 89.

The invention is not, of course, limited to the modificationsillustrated herein, and may be further modified and changed by persons skilled in the art without departing from its spirit and scope, as defined in the appended claims.

What is claimed is:'

1. An oscillatory system comprising a coil, a winding in circuit therewith, and a magnetome chanical vibrator energizgd by the coil, the vibrator being adaptedto vibrate mechanically by magnetostriction, means cooperatively related to the vibrator so that its electrical conductivity varies in accordance with the magnetostrictive deformations of the vibrator, means connecting the first-named means in an electric circuit, a source of energy for the circuit, and a winding in the circuit coupled to the first-named winding.

2. An electric system having, in combination, two circuits each having a coil, a source of energy for one of the circuits, the coils being coupled together, a magnetostrictive body, means connected in one of the circuits and cooperatively related to the body so that its electrical conductivity varies in accordance with the m gnetostrictive deformations of the body, the other circuit having an energizing coil for the magnetostrictive body, whereby energy is transferred from one circuit to the other, a further coil in inductive relation to'the energizing coil, and a load circuit electrically connected to the lastnamed coil.

3. An electric system having, in combination, two circuits each having, a coil, a source of energy for one of the circuits, the coils being coupled together, a magnetostrictive body, and means connected in one of the circuits and cooperatively related to the body so that its electrical conductivity varies in accordance with the magnetostrictive deformations of the body, the other circuit having an energizing coil for the magnetostrictive body, whereby energy is transferred from one circuit to the other circuit.

GEORGE W. PIERCE. 

